Certain indole derivative compounds such as ellipticine derivatives and aza-ellipticine derivatives are already known as intercalating molecules for correcting dysfunctions in gene expression, notably in DNA replication. They have been more specifically described for treating diseases such as cancer, leukemia or AIDS (see in particular patents FR 2,627,493, FR 2,645,861, FR 2,436,786).
Concerning current treatments for AIDS, the various approaches aimed at reducing viral load in patients infected by HIV utilize molecules intended to inhibit the enzymatic activity of viral reverse transcriptase or of the protease involved in virus protein maturation. Regarding reverse transcriptase inhibitors, these can be nucleosidic (NRTIs), non-nucleosidic (NNRTIs) or nucleotidic in nature. The purpose of using these compounds is to prevent a DNA copy of the retroviral genome from being produced and, consequently, from being integrated into the genome of the host cell. Protease inhibitors (PIs) interfere with the proper maturation of viral proteins and cause the production of incomplete particles with altered infectious capacities. There is another type of anti-retroviral compound used for its ability to prevent viruses from entering the cell. These entry inhibitors can be either peptides that interfere with the fusion of viral glycoproteins gp41 or gp120 with the membrane of CD4 cells or molecules that target HIV cellular co-receptors CCR5 and CXCR4. The absence of cellular proteins resembling HIV integrase has also been exploited to develop novel anti-HIV molecules that inhibit this enzymatic activity. Although a number of integrase inhibitors are in the clinical trial phase, no molecule is yet available on the market.
Concerning cancers, more than 90% originate from the malignant transformation of epithelial cells and, in most cases, cancer patient mortality is not due to the primary tumor but to metastases that derive from it. This malignant progression leading to metastases and their subsequent invasion initially involves the loss of cellular adhesion and an increase in motility, thus allowing invasive cells to escape from the initial site and to colonize target tissues. In a great number of cases, it appears that the tumor progression mechanism is associated with aberrant slicing that leads to the formation of isoforms with proto-oncogenic activity. Currently, no molecule with anti-invasive functionality exists. This underlines the lack of a genuinely powerful means of fighting metastases. The current absence of this type of molecule on the market confers on them an economic potential of the highest order.
Duchenne muscular dystrophy (DMD) is a serious illness resulting from mutations in the dystrophin gene. The absence of this protein leads to degeneration of skeletal and cardiac muscles. Several therapeutic strategies are currently envisaged, including so-called exon skipping, whose principle is to cut from dystrophin the internal exon carrying the mutation, thus allowing the production of a shorter but functional dystrophin.
Laminopathies are disorders that lead to an unsatisfactory quality of life, require expensive care and, in many cases, can lead to premature death (i.e., laminopathies of striated muscle tissues and laminopathies characterized by premature aging). Laminopathies are caused by functional changes in lamins, ubiquitous proteins located in the cell nucleus, and in their molecular partners. Most cases of progeria, or early-aging syndrome, are caused by a recurring de novo point mutation (c.1824C>T, “G608G”) occurring in exon 11, i.e., in the part of the gene specifically coding for lamin A. It has been shown that this mutation alters splicing mechanisms and leads to the production of a truncated lamin A precursor (“progerin”, LaminΔ50, p.V607_Q656del), exerting a dominant negative effect on residual wild proteins.
In all these pathologies, the splicing process plays a key role. This intracellular splicing process consists of eliminating introns in pre-messenger RNAs to produce mature messenger RNAs that can be used by the translation mechanism of the cell (SHARP, Cell, vol. 77, p. 805-815, 1994). In the case of alternative splicing, the same precursor can be the source of messenger RNAs coding for proteins with distinct functions (BLACK, Annu. Rev. Biochem. vol. 72, p. 291-336, 2003). The precise selection of 5′ and 3′ splicing sites is thus a mechanism that generates diversity and that can lead to the regulation of gene expression according to the type of tissue or during the development of an organism. The factors involved in this selection include a family of proteins called SR, characterized by the presence of one or two RNA recognition motifs (RRM) and a domain rich in arginine and serine residues called an RS domain (MANLEY & TACKE, Genes Dev., vol. 10, p. 1569-1579, 1996). By binding to short exon or intron sequences of the pre-mRNA, called ESE (exonic splicing enhancer) or ISE (intronic splicing enhancer), SR proteins are able to activate, in a dose-dependant manner, sub-optimal splicing sites and to enable the inclusion of exons (GRAVELEY, RNA, vol. 6, p. 1197-1211, 2000). The activity of an SR protein in alternative splicing is specific insofar as the inactivation of the corresponding gene is lethal (WANG et al., Mol. Cell, vol. 7, p. 331-342, 2001).
Sequencing of the human genome and analysis of EST (expressed sequence tag) banks has revealed that 65% of genes are expressed in the form of alternatively spliced variants (EWING & GREEN, Nat. Genet., vol. 25, p. 232-234, 2000; JOHNSON et al., Science, vol. 302, p. 2141-2144, 2003). This mechanism is thus a favored target of modifications that can affect the factors involved in regulating splicing and of mutations that affect the sequences necessary for this regulation. At present, it is estimated that roughly 50% of the point mutations responsible for genetic diseases induce aberrant splicing. These mutations can interfere with splicing by inactivating or creating splicing sites, but also by modifying or generating regulating elements such as splicing enhancers or splicing silencers in a particular gene (CARTEGNI et al., Nat. Rev. Genet., vol. 3, p. 285-298, 2002; TAZI et al., TIBS, vol. 40, p. 469-478, 2005).
The strategies currently developed to correct these splicing defects rest on the use of various types of molecules (TAZI et al., cited above, 2005).
One strategy aimed at developing novel molecules to correct or eliminate abnormal splicing, for example, rests on the overexpression of proteins that interfere with this type of splicing (NISSIM-RAFINIA et al., Hum. Mol. Genet., vol. 9, p. 1771-1778, 2000; HOFINANN et al., Proc. Natl. Acad. Sci. U.S.A., vol. 97, p. 9618-9623, 2000).
Other strategies rest on the use of antisense oligonucleotides (SAZANI et al., Nat. Biotechnol., vol. 20, p. 1228-1233, 2002; SAZANI & KOLE, Prog. Subcell. Biol., vol. 31, p. 217-239, 2003) or of PNA (CARTEGNI et al., Nat. Struct. Biol., vol. 10, p. 120-125, 2003) enabling, respectively, the inhibition or activation of a splicing event.
Yet another strategy rests on the identification of compounds that influence the splicing efficiency of the pre-mRNA of interest (ANDREASSI et al., Hum. Mol. Genet., vol. 10, p. 2841-2849, 2001).
Lastly, a strategy based on the use of trans-splicing to replace mutant exons has been described (LIU et al., Nat. Biotechnol., vol. 20, p. 47-52, 2002).
One of the disadvantages of the developed strategies cited above to correct or eliminate abnormal splicing is their production cost. Indeed, the cost of producing antisense oligonucleotides that must be modified to improve their stability, and that of PNA molecules, is high.
Another disadvantage of the developed strategies cited above is that they require the use of expression vectors, such as, for example, for the strategy based on the use of trans-splicing.
International application WO05023255, under French priority of requests FR0310460 and FR0400973, filed by the Applicant, disclosed the use of indole derivatives to treat diseases related to the pre-messenger RNA splicing process in the cell.
Thus it was recently shown that certain indole derivatives prove particularly effective in treating metastatic cancer and in treating AIDS (BAKKOUR et al., PLoS Pathogens, vol. 3, p. 1530-1539, 2007).
However, the compounds described have a flat structure with four rings that have the disadvantage of intercalating between DNA bases and can thus lead to cellular toxicity.